Bootstrap 5.1.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 148821 bytes (145.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 59733 bytes (58.3k, 40%).

After GZIP compression these minified files vary in size:

unpkg	22468 bytes (21.9k)	CDN
gzip -6 (default)	15953 bytes (15.6k)	local copy
jsdelivr	15924 bytes (15.6k)	CDN
cdnjs	15885 bytes (15.5k)	CDN
gzip -9	15875 bytes (15.5k)	local copy
libdeflate -12	15353 bytes (15.0k)	local copy
7zip -mx=9 -tgzip	15352 bytes (15.0k)	local copy
zultra	15328 bytes (15.0k)	local copy
kzip -s0 -rn -b2	15304 bytes (14.9k)	local copy
pigz -11 -n	15300 bytes (14.9k)	local copy
Zopfli	15292 bytes (14.9k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.1.1.min.js (or via HTTPS)

You will automatically get the smallest Bootstrap 5.1.1 file, ETag caching is available and
if your browser doesn't support GZIP decompression then the uncompressed version will be sent.

Currently best Zopfli settings

Save 593 bytes by using my Bootstrap 5.1.1 Zopfli version instead of the best available CDN (3.88% smaller than cdnjs, 15292 vs. 15885 bytes):

Download

You can use my super-compressed files for whatever purpose you like as long as you respect the library's original license agreement.
There are no restrictions from my side - but please avoid hot-linking if you run a high-traffic website.

These command-line settings yielded the best compression ratio so far (Linux version of zopfli-krzymod):
zopfli --i1000000 --mb8 --mls4096 --bsr17 --lazy --ohh

(found September 14, 2021)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	4096	--mls4096
block splitting recursion	17	--bsr17
lazy matching in LZ77	yes	--lazy
optimized Huffman headers	yes	--ohh
initial random W for iterations	1	--rw1
initial random Z for iterations	2	--rz2

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v5.1.1/dist/js/bootstrap.min.js --location | md5sum
53f7f752152ec85a9b53e66e807930aa -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.1.1.min.zopfli.js.gz | md5sum
53f7f752152ec85a9b53e66e807930aa -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v5.1.1/dist/js/bootstrap.min.js --location | sha1sum
530ca54dfdb4d3e7f496fd782d87aaf0f1696946 -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.1.1.min.zopfli.js.gz | sha1sum
530ca54dfdb4d3e7f496fd782d87aaf0f1696946 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
unpkg	22468 bytes	53f7f752152ec85a9b53e66e807930aa	(invalid)
jsdelivr	15924 bytes	53f7f752152ec85a9b53e66e807930aa	September 13, 2021 @ 14:08
cdnjs	15885 bytes	53f7f752152ec85a9b53e66e807930aa	(invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available Bootstrap versions at minime.stephan-brumme.com:

5.2.3, 5.2.2, 5.2.1, 5.2.0,
5.1.3, 5.1.2, 5.1.1, 5.1.0,
5.0.2, 5.0.1, 5.0.0,
4.6.0,
4.5.3, 4.5.2, 4.5.1, 4.5.0,
4.4.1, 4.4.0,
4.3.1, 4.3.0,
4.2.1, 4.2.0,
4.1.3, 4.1.2, 4.1.1, 4.1.0, 4.0.0,
3.4.1, 3.4.0,
3.3.7, 3.3.6, 3.3.5, 3.3.4, 3.3.2, 3.3.1, 3.3.0,
3.2.0,
3.1.1, 3.1.0,
3.0.3, 3.0.2, 3.0.1, 3.0.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, D3, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
15292 bytes	-1 byte	zopfli --i1000000 --mls4096 --bsr17 --lazy --ohh	September 14, 2021 @ 21:17
15293 bytes	-3 bytes	zopfli --i1000 --mls128 --bsr19 --lazy --ohh	September 14, 2021 @ 10:54
15296 bytes	-1 byte	zopfli --i1000 --mls128 --bsr8 --lazy --ohh	September 14, 2021 @ 10:54
15297 bytes	–	zopfli --i100 --mls512 --bsr16 --lazy --ohh	September 13, 2021 @ 16:38

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on September 15, 2021 @ 04:20.

Heatmaps

This Zopfli heatmap visualizes how compression changes when modifying the --bsr and --mls parameter.
Cell's contents is the best filesize achieved (in bytes, hover with mouse over cells to see number of iterations).

Good parameters are green, bad are red. The best and worst are bold as well.
The brightness of the blue background color indicates how many iterations were processed:
10,000 or 1,000,000.

bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
2	15309	15309	15310	15309	15310	15310	15311	15310	15303	15307	15306	15306	15307	15305	15310
4	15299	15300	15300	15304	15300	15302	15304	15303	15299	15295	15294	15296	15299	15302	15300
6	15302	15302	15303	15302	15301	15300	15303	15302	15299	15295	15294	15296	15302	15301	15301
7	15298	15297	15296	15301	15300	15301	15294	15302	15296	15296	15294	15294	15300	15302	15303
8	15299	15294	15299	15301	15299	15302	15295	15302	15303	15295	15294	15296	15298	15297	15298
9	15301	15301	15299	15301	15299	15300	15295	15302	15294	15295	15293	15296	15296	15301	15304
10	15302	15301	15301	15301	15301	15299	15300	15303	15295	15294	15293	15295	15303	15300	15299
11	15298	15301	15297	15298	15299	15300	15299	15301	15295	15295	15293	15296	15302	15299	15298
12	15303	15303	15301	15303	15303	15300	15295	15302	15300	15295	15294	15296	15297	15299	15303
13	15301	15300	15301	15301	15299	15300	15295	15294	15299	15295	15295	15295	15301	15299	15316
14	15299	15300	15299	15294	15300	15300	15295	15294	15297	15295	15294	15294	15301	15301	15300
15	15301	15300	15299	15301	15301	15302	15303	15302	15295	15295	15294	15296	15299	15296	15299
16	15299	15300	15300	15301	15301	15300	15293	15294	15292	15294	15294	15295	15297	15298	15299
17	15298	15307	15296	15298	15300	15300	15301	15294	15295	15294	15294	15292	15301	15301	15301
18	15298	15295	15298	15301	15301	15299	15294	15294	15297	15294	15294	15294	15297	15301	15301
19	15301	15303	15301	15301	15299	15300	15292	15302	15294	15295	15294	15296	15301	15299	15300
20	15298	15301	15297	15298	15300	15301	15294	15294	15294	15294	15294	15295	15297	15300	15300
21	15300	15301	15298	15302	15300	15301	15295	15300	15299	15294	15293	15294	15297	15300	15300
22	15300	15301	15299	15303	15299	15300	15301	15295	15295	15295	15293	15295	15297	15300	15300
23	15301	15300	15300	15303	15299	15301	15295	15294	15299	15294	15294	15296	15297	15301	15301
25	15300	15300	15299	15301	15301	15300	15295	15303	15296	15295	15294	15296	15300	15300	15303
30	15298	15303	15299	15294	15299	15302	15295	15294	15299	15295	15294	15294	15298	15297	15299
40	15299	15301	15300	15296	15298	15301	15303	15301	15295	15294	15294	15296	15296	15299	15299

Due to the Monte Carlo design of my search algorithm, not all parameters have reached the same number of iterations yet:

Iterations	Min. Bytes	Reduction	Coverage
100	15297 bytes	–	100%
1,000	15293 bytes	-4 bytes	100%
10,000	15293 bytes	–	100%
100,000	15293 bytes	–	2.61%
1,000,000	15292 bytes	-1 byte	2.61%
10,000,000	–	–	–

KZIP has far less options available for tuning/optimization. I only played around with the number of blocks (parameter -n):

Blocks	Min. Bytes	Compared To Best Zopfli	Compared To Best KZIP
(any)	15390 bytes	+98 bytes (+0.64%)	+86 bytes
1	15392 bytes	+100 bytes (+0.65%)	+88 bytes
2	15304 bytes	+12 bytes (+0.08%)	–
3	15333 bytes	+41 bytes (+0.27%)	+29 bytes
4	15366 bytes	+74 bytes (+0.48%)	+62 bytes
5	15374 bytes	+82 bytes (+0.54%)	+70 bytes
6	15409 bytes	+117 bytes (+0.77%)	+105 bytes
7	15454 bytes	+162 bytes (+1.06%)	+150 bytes
8	15472 bytes	+180 bytes (+1.18%)	+168 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
However, support for Brotli is constantly growing - for example, your browser actually supports it !

Algorithm	Program	Parameters	Size	Compared To Best Zopfli
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	12857 bytes	-2435 bytes (-15.92%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	13234 bytes	-2058 bytes (-13.46%)
Brotli (Wikipedia)	brotli	brotli -q 11	14216 bytes	-1076 bytes (-7.04%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	14917 bytes	-375 bytes (-2.45%)
LZMA2 (Wikipedia)	xz	xz -9	15068 bytes	-224 bytes (-1.46%)
Zstandard (Wikipedia)	zstd	zstd -19	15188 bytes	-104 bytes (-0.68%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	15415 bytes	+123 bytes (+0.80%)

Detailled Analysis

I wrote a DEFLATE decoder in Javascript. Click the button below to start a client-side analysis of the smallest gzipped files (may take a second):

Load and Parse Data

Notes: pigz is a fast open source multi-threaded implementation of gzip written by one of the original authors of gzip.
However, when using compression level 11, pigz actually switches to the slower Zopfli algorithm and isn't multi-threaded anymore.
KrzyMOD's extensions to Zopfli offer the highest level of configuration and is therefore used for my brute-force search.
Ken Silverman wrote the closed-source KZIP compression program and Jonathon Fowler ported it to Linux.
Defluff was created by Joachim Henke; DeflOpt is a tool by Ben Jos Walbeehm.

website made by Stephan Brumme in 2015 and still improving in 2026.
all timestamps are displayed in central european time. see my changelog.
no flash, not even images or external css files - and everything squeezed into a single html file.
which was handsomely compressed before releasing it into the wild internet - obviously.

please visit my homepage and my blog, too.
email: minime (at) stephan-brumme.com

All trademarks are property of their respective owners. You know, the boring legal stuff.